1. Field of the Invention
The present invention relates to an electrostatic image generating apparatus, such as a laser printer, using a continuous strip of paper.
2. Description of the Related Art
There are used various electrostatic image generating apparatus, including electrostatic copiers, laser printers, laser facsimile machines and the like. A typical electrostatic image generating apparatus uses a photosensitized drum with a photosensitized surface made of photoconductive insulating material. A charging unit is used to place a uniform electrostatic charge over the photosensitized surface preparatory to imaging. Then, a desired light image is either projected by an optical system or drawn by a laser beam scanner on the photosensitized surface, to form an electrostatic latent image on the surface. Thereafter, the latent image is developed with a developing material, powdery material referred to in the art as toner, to form a toner image on that surface. The toner image is then transferred to a support surface, such as a surface of a sheet or strip of paper. The paper is then transported to a fixing unit, where the transferred toner image is fixed onto the surface of the paper.
Some laser printers which may be used, for example, with a computer system are designed to be capable of printing on a continuous strip of paper, such as a strip of fan fold paper having regularly spaced perforations along its longitudinal marginal edges. Where a continuous strip of paper is used, the portion of the paper strip running between the photosensitized drum and the fixing unit often has to be kept tensioned at an acceptable tension level. Thus, some of such laser printers include a tension unit for applying a predetermined level of tension to that portion of the paper strip.
It is often desired, however, to use with one laser printer various types of paper strips having acceptable tension ranges different from each other. In such case, the predetermined tension level provided by that laser printer may happen to be too high or too low for the paper strip that the operator wish to use. Acceptable tension level may vary depending on thickness of the paper strip, type of material of the paper strip, whether the paper strip is folded or not and whether the paper strip has transverse cutting lines of fine perforations or not. Too high a tension level may result in a breakage or tear of the paper strip, while too low a tension level may lead to frequent paper jams in the printer. In particular, where a strip of fan fold paper is used, too low a tension level is likely to cause a paper jam because such tension level often fails to make the strip of fan fold paper straight enough for smooth operation of the printer. This practically prevents use of a wide range of paper strips with one laser printer.
Accordingly, there has been a long desire for an electrostatic image generating apparatus using a continuous strip of paper, in which different types of continuous paper strips having different acceptable tension ranges may be conveniently used with that apparatus.